How to render a collection instance but not the original collection in blender 2.8?
I have managed a way to help you with this issue. Yesterday I was trying the same thing and I realized a way to not render the original collection and only the models created with a collection instance tool.

What you need to do is put all of your original “Assets” inside another collection. Then turn off the eye icon in all of them (including the bigger collection parent) and then turn off also the camera icon (for it not to appear on the render) but only in the parent collection and not on the assets themselves.

This means that blender will not render anything that is inside that collection but still if the objects inside are on it will interpret as if they were rendering so it will render the instances of that particular asset.

If it is not clear enough I will share an image :p

The prop collection is filled with my original assets and the workspace collection is filled with the instances created with the collection instance tool




If its is not clear repost and i will try to explain better